The present invention concerns a polymer blend which is useful for producing fibers, coatings and films.
Such a blend generally comprises 5 to 95 parts by weight of poly(2,6-dimethyl-1,4-phenylene) ether, 95 to 5 parts by weight of a polymer other than polyamide, which is immiscible therewith, and a component (a compatibilizer) which enhances the compatibility of said polymers.
The invention also concerns a process for the preparation of novel polymer blends and new products containing said blends.
Poly(2,6-dimethyl-1,4-phenylene) ether (PPE) is formed by alternating methyl-substituted phenyl rings and ether groups. PPE is an almost amorphous thermoplastic polymer. Its glass transition temperature (T.sub.g) is generally in the range from 205 to 210.degree. C. Its degree of crystallinity is typically a few percent. The melting point of the crystals is in the range from 262 to 267.degree. C. (Polym. Prepr. 1971, 12, 317). It should be pointed out that a particular advantage of PPE lies in the fact that the polymer behaves plastically at very low temperatures, even at -200.degree. C. The heat resistance of PPE is high (HDT/A 174.degree. C.).
Since PPE is very aromatic it is also rather rigid. Therefore, PPE is an interesting polymeric blending component for providing stiffness and for increasing strength. However, the melt index of PPE is very high; in other words, it is almost impossible to process it by using traditional polymer melt processing techniques, such as injection moulding or extrusion. Because of the high melt viscosity, the processing temperature should be increased over 300.degree. C., at which temperature it becomes difficult to blend the polymer with other polymers which have lower melting points. Furthermore, even in oxygen-free conditions, PPE is thermally stable only at temperatures of up to about 250.degree. C., and when the temperature is raised over 300.degree. C. gelling will be initiated.
It is known in the art that the viscosity of polymers can generally be lowered by using plasticizers. Plasticizers can also be used to improve processibility, flexibility and elasticity (ASTM D 833). Proper action of the plasticizer requires that the polymer and the plasticizer be sufficiently miscible with each other. Generally, the plasticizer should be soluble in the polymer which is to be plasticized or vice versa. Each polymer has its own specific plasticizer, because dissolution depends on the chemical compatibility of the polymer which is to be plasticized and the dissolving admixture.
It is also known in the art that when a very small amount of a plasticizer is used, which is completely miscible with the polymer, it is possible to increase the stiffness, strength and toughness of the polymer. This phenomenon is called "antiplasticizing". Generally, said phenomenon and its basis for polymers have been described extensively in the literature (Adv. Chem Ser., 48, 185 (1965), J. Appl. Polym. Sci., 11, 211 (1967), J. Appl. Polym. Sci., 11, 227 (1967), J. Macromol. Sci.-Phys., B1, 433 (1967), Polym. Eng. Sci., 9, 277 (1969), J. Polym. Sci. Polym. Lett. Ed., 7, 35 (1969), Polym. J. 4, 23 (1973), Polym. J., 4, 143 (1973), J. Macromol. Sci.,-Phys., B14, 251 (1977), J. Pol. Sci., J. Appl. Poly. Sci., 23, 1935 (1979), J. Appl. Poly. Sci., 11, 2553 (1967), J. Appl. Poly. Sci., 17, 2173 (1973), J. Appl. Phys., 43,4318, (1972), A. Bondi, Physical Properties of molecular Crystals, Liquids and Glasses, Wiley, 1968, J. Polym. Sci. Polym. Lett. Ed., 21, 1041 (1983), ACS Symp. Ser., 223, 89 (1983), J. Pol. Sci., Part B, 25, 957 (1987), J. Pol. Sci., Part B. 25, 981 (1987), J. Pol. Sci., Part B, 25, 1005 (1987), Macromolecules 21, 1470 (1988)). Said publications deal with the influence of the admixture on the mechanical properties, volume and glass transition of the polymer, but they do not address, for example, the influence of the admixture on the compatibility of the polymer with another polymer.
PPE is conventionally made processible by using a polymer, viz. polystyrene, as plasticizer. Polystyrene is blended with PPE, which is miscible with polystyrene at all mixing ratios. The properties of the PPE/PS-blend so formed can be controlled by adjusting the mixing ratios. Polystyrene lowers the viscosity of the PPE and improves the flow properties of the polymer blend. PPE is in a corresponding way at least partially miscible with and soluble in polymers which are similar to polystyrene, such as isotactic polystyrene, poly(p-methylstyrene), poly(.alpha.-methylstyrene), copolymers of halostyrene and styrene, poly(2-methyl-6-phenyl-1,4-phenylene) ether, and poly(2-methyl-6-benzyl-1,4-phenylene) ether.
Plasticizing of PPE with high impact polystyrene (HIPS) produces a blend, which, due to its impact strength and other properties, is of great importance as a structural polymer material in components used in the automotive industry and in the industry producing electrical appliances. PPE/HIPS blends are processible by conventional melt processing methods. The proportion of HIPS in the blends can vary widely depending on the specific application. However, it is often 50 to 80 wt-%. Stiffness and tensile strength decrease as the concentration of HIPS increases, as will be shown in an example given below. When the proportion of HIPS is diminished, the processing of the polymer blend becomes more difficult.
U.S. Pat. No. 4,826,919 teaches further improvement of the flow properties of PPE/HIPS blends by using small amounts of triphenyl phosphate, mineral oil, silicon oil and polyolefins. However, the mechanical properties, such as the impact strength, tensile strength and heat resistance, are impaired by such additions.
The prior art, J. Pol. Sci., Part B, 25, 957 (1987), J. Pol. Sci., Part B, 25, 981 (1987), J. Pol. Sci., Part B, 25, 1005 (1987), Macromolecules 21, 1470 (1988), also teaches plasticizing PPE by using oligomeric plasticizers. These substances have been exemplified by tricresyl phosphate, Kronitex 50 (an organic phosphate), di-2-ethylhexyl phthalate, dioctyl sebacate, dimethyl sebacate, and dibutyl sebacate. Said plasticizers will lower the glass point while, at the same time, the stiffness is impaired at room temperature or temperatures above that. In other words, said oligomeric admixtures act in the same way as conventional plasticizers; no essential stiffening or antiplasticizing has been noticed at said conditions.
In addition to the blends formed by PPE and polymers miscible with it, in particular polystyrene, it is known that PPE can be blended with polymers which are immiscible with it. Thus, polyamide 6 (PA6) can be used in amounts of 1 to 6 wt-% for improving the flow properties of PPE. On a molecular level, however, polyamide and PPE do not form miscible blends. The prior art methods for preparing PPE/PA blends are therefore based on grafting PPE with maleic anhydride, which reacts with the terminal amine groups of the polyamide. (Campbell, J. R., Pol. Eng. Sci. Vol. 30(1990) No. 17, 1056). Blends of PPE and PA are used particularly in the automotive industry for applications requiring good chemical stability.
PPE blends with polyolefins have been compatibilized with, for instance, di-block copolymers of saturated styrene and butadiene (EP 0 358 993) or with polypropylene grafted with polystyrene (EP 0 352 057 and EP 0449 087). Polymers containing glycidyl methacrylate or maleic anhydride are known to be used for compatibilizing PPE-blends. The aforementioned functional groups can react with the terminal hydroxy groups of PPE (EP 0 356 194 and DE 39 26 292).
The prior art also includes teachings of PPE blends formed with polyesters. Polymer 32 (1991) pp. 2150-2154 discloses a complex blending combination, wherein PPE, poly(butylene terephthalate) (PBT), polycarbonate (PC) and a triblock polymer of styrene-ethylene butylene-styrene (SEBS) form a structure, in which PBT is the continuous phase, PPE is modified with the SEBS-elastomer and polycarbonate is present at the interface between the PPE and the PBT.
Furthermore, Polymer 33 (1992) pp. 4322-4330 discloses how aromatic liquid crystalline polymers (LCP) can be used for improving the flow properties of PPE. LCP is not miscible with PPE, but the low melt viscosity of the LCP at high temperatures allows for processing of the PPE. However, the immiscibility gives rise to poor adhesion between the phases. The mechanical properties are therefore not good.
Several oligomeric solvents for PPE are known in the art: benzene, toluene, ethylbenzene, chlorobenzene, chloroform, carbon tetrachloride, trichloroethylene and dichloromethane (Polymer, Vol. 28 (1987), 2085). Decaline has also been suggested as a solvent for PPE (Janeczek, H., Polymer, 19 (1987) January, 85). Furthermore, .alpha.-pinene has been mentioned. With the help of some of the above mentioned solvents, partial crystallization of the PPE can be achieved.
PPE is generally only partially soluble in aliphatic hydrocarbons, acetone, several alcohols and tetrahydrofurane. PPE exhibits good resistance against water, acids and alkalis. (Kroschwitz, High Performance Polymers and Composites, John Wiley & Sons 1991, U.S.A). A homogeneous miscible mixture is obtained from toluene and PPE by keeping the proportion of PPE at a maximum of 40 wt-%, when the temperature is raised to 110.degree. C. When the mixture is cooled, some crystallization of the solvent and PPE can possibly be observed (J. Pol. Sci. Pol. Phys. Ed. Vol. 15 (1977) 167).
A homogeneous solution of PPE and methylene chloride can be prepared at room temperature by keeping the concentration at a maximum of 20 wt-%. Bromochloromethane and ethylene bromide and .alpha.-pinene and cis- and trans-decaline have also been mentioned as solvents for PPE which can induce crystallization (Pol. Letters, Vol.7 (1969), 205).
In summary, it can be stated on basis of the prior art that it is possible to obtain mechanically satisfying blends of PPE with other polymers
primarily by using polystyrene and derivatives thereof, PA1 by using block polymers containing styrene as compatibilizers for, e.g., polyolefins, PA1 by utilizing terminal group chemistry, PPE being chemically modified with an active group, which reacts with the other polymer, or PA1 by utilizing the reactivity of the terminal groups of PPE. PA1 A is a group which contains at least one 3- to 7-membered ring group capable of forming ring-to-ring interactions with the phenyl rings of the poly(2,6-dimethyl-1,4-phenylene) ether, PA1 B is a polar group, PA1 i is an integer 1 to 20, and PA1 j is an integer 0 to 20, PA1 the sum of i and j is equal to or greater than 2; PA1 the melting point of compound C is over 50.degree. C. and its boiling point is over 200.degree. C. (at 760 mmHg) and PA1 compound C is capable of at least partially dissolving poly(2,6-dimethyl-1,4-phenylene) ether.
Plasticizing of PPE by using oligomeric additives and their influence on the mechanical and physical properties as well as on gas permeability have been studied in the prior art.
The fact that PPE is easily miscible with polystyrene and its derivatives is primarily caused by the formation of a miscible blend. But if PPE is blended with other polymers (which are immiscible with it), such as with polyethylene, according to the prior art the properties of the blends are generally not good, the mechanical strength remains poor and the components of the blends are strongly phase-separated.
For the above reasons there has already for a long time existed a need in polymer technology for providing a way of generally compatibilizing PPE with any matrix polymer, in particular in cases when the miscibility of PPE with a polystyrene block cannot be relied upon.